A hallmark of biliary tract disease is a decrease in the tone of gallbladder smooth muscle (GBSM), and a decrease in the responsiveness of GBSM to excitatory agonists. Despite the importance of GBSM excitation, contraction (EC) coupling, little is known about this process. The objectives of this proposal are to establish the mechanisms for GBSM excitation and how this translates to muscle contraction. The first Specific Aim is to determine the cellular mechanisms that are responsible for electrical rhythmicity in GBSM. Our preliminary data indicate that the gallbladder rhythmicity departs radically from the mechanisms that dominate control in other parts: of the GI tract. The novel possibility that the action potential of GBSM is terminated by ERG K+ channel activation will be explored. The ERG channel is a target of a number of clinically relevant drugs including the prokinetic agent, cisapride. We will be particularly interested in determining whether the GBSM ERG channel differs pharmacologically from the cardiac muscle channel, with the hopes of ultimately guiding studies on the development of GBSM specific ERG blockers. The second Specific Aim will determine the mechanisms by which excitatory agonists such as acetylcholine and CCK stimulate GBSM, with a focus on non-selective cation channels, specifically: TRP channels. The role of K+ channel inhibition in the excitatory: effects of agonists will also be determined. The third Specific Aim will determine how excitatory agonists alter the pattern of calcium signaling in GBSM. We will test the novel concept that excitatory agonists shift calcium signaling from sparks - a smooth muscle relaxation mechanism through activation of K+ channels - to calcium waves, a signal that contributes to contraction. We propose an integrated approach using state-of-the-art techniques to determine GBSM function from single molecules to the intact tissue. Together with our previous studies on gallbladder nerves, we expect to provide a comprehensive view of gallbladder function, which should illuminate new pathways to handle biliary tract disease.